Fossil corals from the Enriquillo Valley provide a unique opportunity to examine sub-annual to century scale climate variation within the time period of 5000-8000 years bp. Comparison of past climate variations with data from modern corals reveals long term global climate patterns.

In April of 1996, 25 samples of Holocene coral were collected from a well preserved fossil fringing reef in the southwestern interior of the Dominican Republic, and ten cores of living coral were extracted from coral heads offshore of Parque del Este in the southeastern part of the country. Montastraea annularis and Siderastrea siderea are equally represented in the specimen population. Yearly coral growth rates were measured along the axis of maximum skeletal extension as revealed by X-radiography methods. The oldest of the modern cores dates back to 1927 while the Holocene record is represented by approximately 950 years of coral growth. Average growth rates are 9.236 mm/year for fossil Montastraea and 3.838 mm/year for Siderastrea. Modern growth rates of both species are less, at 8.422 mm/year for Montastraea and 2.601 mm/year for Siderastrea. Preliminary time series analyses reveal peak growth periodicities at both 5 and 10 to 15 year frequencies.

Fluctuations in these coral growth-rate patterns reflect a variety of environmental forces, such as: changing patterns of light levels (including indirect effects of rainfall, depth gradients and cloud cover), temperature, food availability, coral age, and sedimentation rates. Fluctutations in the length of sub-annual seasons are ascertained from the contrast between and relative proportion of high and low density bands. Evidence for lunar cyclicity in inter-annual density banding is proposed.